The present invention relates generally to television receivers and, more particularly, to an improved circuit for processing the luminance signal developed at the output of the video detector of a television receiver.
The output of the video detector of a color television receiver develops a luminance signal which, after suitable processing, is used to modulate the cathode ray tube of the receiver according to the brightness of the reproduced scene. Thus, the luminance signal used in color television transmissions is quite similar to the video signal employed for standard monochrome transmissions. Traditionally, the main function of the television receiver circuitry used to process the luminance signal, commonly referred to as the luminance channel, between the video detector and the cathode ray tube has been that of signal amplification. In this regard, luminance channel designs composed of one, two or three stages of amplification have been used for controllably providing the desired brightness signal to achieve a desired level of signal contrast. A secondary function of the luminance channel has been to introduce a specific time delay in the luminance signal to compensate for the time delay which the chrominance signal experiences due to the narrower bandwidth of the chrominance channel.
More recently, attempts have been made to incorporate a signal peaking function in the luminance channel. As used herein, the term "signal peaking" refers to the technique of accentuating transistions in the luminance signal relative to flat field portions thereof to increase the sharpness of the reproduced image. Typically, derivatives of the full bandwidth luminance signals have been used to derive the necessary peaking signals. In order to accomplish the various functions of the luminance channel prior art luminance signal processing circuits typically consist of a series of cascaded stages each operating from its own source of DC potential to perform its respective function. Such an arrangement results in excessive power consumption and an inefficiently operating circuit. In addition to this problem, prior art luminance channel peaking circuits frequently accentuate signal transitions representing noise in the flat field portions of the luminance signal thereby degrading the clarity of the reproduced image. Yet further, prior art luminance channel peaking circuits often provide excessive white going peaking signals which cause an undesirable blooming in the reproduced picture.
It is, accordingly, a general object of the present invention to provide an improved circuit for processing the luminance signal in a monochrome or color television receiver.
It is a more specific object of the invention to provide a luminance signal processing circuit which is characterized by reduced power consumption and which includes a dynamic noise processed peaking system which accentuates luminance transitions but not noise signal spikes occurring during flat field portions of the luminance signal.
A further object of the invention is to provide such a system wherein blooming due to excessive white going peaking signals is reduced and wherein the peaking or sharpness level as well as the brightness or contrast of the reproduced image are independently controllable by the viewer.